Certain known platform modules are normally transported and installed in a body of water using vessels equipped with lifting systems. These systems call for the use of relatively high-cost equipment, involve considerable risk by having to lift relatively extremely heavy platform modules, and are seriously limited by environmental (sea bed, sea, and weather) conditions.
A so-called ‘float-over’ technique has recently been developed whereby a barge is used to support at least one platform module. The barge is moved into position between the legs of the supporting structure in a body of water. The platform module is then moved vertically by the combined operation of mechanical devices (heavy-duty hydraulic jacks), and by adjusting the ballast (draft) of the barge.
The barge is fixed to the supporting structure by a known mooring system configured to limit horizontal movement of the barge.
This type of mooring system, however, fails to limit vertical movement of the barge, which for the most part is uncontrollable and dependent on water and weather conditions.
Vertical movement of the barge makes the barge relatively difficult to connect the platform module to the supporting structure, and to detach the barge completely from the platform. At the connecting stage, vertical movement of the barge may result in the platform module colliding with the supporting structure, thus impairing connection and possibly also damaging both.
As the barge is being detached, on the other hand, vertical movement of the barge may cause barge to impact the installed platform module.
Research into the forces involved at the connecting and detaching stages shows the difficulties posed, mostly in areas with typically unpredictable water conditions, can be overcome by carrying out the connecting and detaching stages as fast as possible.
One known system configured to transfer a platform module from a barge to a supporting structure in a body of water is described in document U.S. Pat. No. 6,027,287 filed by the present Applicant. This system is relatively fast at the connecting and detaching stages, but is unacceptably slow in emergency reversing situations.
Other similar methods are described in EP Patent No. 0097069, U.S. Pat. Nos. 5,403,124, 5,522,680, 6,293,734, 6,347,909 and U.S. Pat. No. 6,981,823, and more recently in PCT Patent Application WO 2010098898 and PCT Patent Application WO 2011028568.